Variable-pitch propeller



Oct. 20, 1953 s. P. BASEVI VARIABLE-PITCH PROPELLER 5 Sheets-Sheet 1 Filed Sept. 14, 1951 Oct. 20, 1953 s. P. BASEVI 2,655,999

VARIABLE-PITCH PROPELLER Filed Sept. 14, 1951 3 Sheets-Sheet 2 4a y F////////// 9 //l l//l/7'0H a I? EASEl/l zm/fl/ Patented Oct. 20, 1 953 UNITED STATES ATENT OFFICE mouth, England, assignor to Rotol' Limited, Gloucester, England, a British company Application September 14, 1951, Serial No. 246,617 In Great Britain September 29, 1950 Claims. 1

This invention concerns variable-pitch propellers and relates to hydraulic propellers of the type in which there is provided a pair of stops to limit the adjustment of the blades towards fine pitch, the stops being displaceable to enable the blades to perform movements within a first range extending beyond the normal pitch range and in a second range extending beyond the first extended range.

The first stop is provided so that when an aircraft is cruising or in high speed flight the pitch of the propeller is prevented from going below a certain value c. g. an angle of 40: this stop is usually called the flight-safety stop. In other conditions of flight it is necessary that the pitch angle be less than the minimum allowed by the flight-safety stop and accordingly the latter must be displaceable to enable the blades to move into the first extended range, Again it is considered necessary that the movement of the blades towards fine pitch within the extended range be again limited (for example, to an angle of and this is done by the second stop referred to the fine-pitch stop.

Under other conditions of flight it may be necessary to use a very fine pitch or even to put the propellers into reverse pitch so that it is further necessary to be able to displace the finepitch stop.

Hitherto, it has been arranged that the two stops be displaced and replaceable together i, e. when the flight-safety stop is removed the finepitch stop is also displaced. Under such circumstances there is no positive means to prevent the propeller moving to its limit of fine-pitch e, g. in reverse or negative pitch before the fine pitch stop has had time to reform.

The object of the present invention is to provide a novel construction of variable-pitch propeller of the type referred to in which when the first or flight-safety stop is displaced the second or fine-pitch stop remains operative. Stated another way the object of this invention is to provide a variable-pitch propeller of the type referred to n which distinct operations are required to remove each of the two stops and such distinct operations may not-be performed at the same time.

According to the present invention a variablepitch propeller comprises a hydraulic pitchchange jack having a movable element adjustabl within a normal range of operation, within a first range extending beyond said normal range and within a second range extending beyond the first extended range, a first stop engageable by the movable element of the jack to prevent its travel beyond the normal range, a second engageable by the movable element of the jack after the element has passed the first stop to prevent its travel beyond the first extended range, means for displacing the stops in succession, restraint means normally preventing said stop-displacing means from acting to displace the second stop and means actuated by the movabl element of the jack through the agency of the second stop, upon engagement of the latter by said element, for rendering the restraint inoperative.

A practical application of the present invention will now be described, by way of example only, with reference to the accompanying drawings whereof:

Figure 1 is a diagrammatic side elevation of a propeller in accordance with the present invention,

Figure 2 is a vertical section of the hub taken on a reduced scale on the line 2-2 of Figure 4;

Figure 3 is a longitudinal section through the pitch change mechanism of the propeller of Figure 1 showing the position of the parts when the blades are in the first extended range of operation; and

Figure 4 is a longitudinal section through the pitch change mechanism of the propeller of Figure 1 showing the position of the parts when the blades are in the normal range of operation,

Referring to the drawings, and mor particularly to Figure 1, the propeller comprises a hub '5 which carries a plurality of blades 5 mounted in sleeves i for pitch-change rotation in Well known manner. Each blade 6 is connected with a piston 8 by a link 9, the piston 8 being axially movable in a cylinder IQ of a double acting jack. Hydraulic fluid may be supplied to the cylinder Ill through either pipe II or pipe l2 by a pump Hi from a sump Hi, the fluid escaping from the exhaust side of the cylinder through pipe 15 to the sump I l. The passage of fluid to, and from, the cylinder i0 is controlled in conventional manner by a constant-speed, or governor, unit generally indicated by the reference numeral 4. When the unit 4 is adjusted, either manually or automatically, pressure fluid is delivered to th cylinder I!) and acting on the piston 8 moves it axially in one direction or the other thereby to adjust the pitch setting of the blades 6 throu h links 9. The unit 4 incorporates a fiyweight governor which is driven by the eng ne and the speed setting of the governor is adjustable by th lever it all in usual manner.

Referring now to Figures 3 and 4, the piston 8 is of annular form and is mounted for sliding movement within the cylinder l upon a stationary sleeve I! coaxially mounted within the cylinder, the piston 8 being formed with a fiange assembly 18 which slides along the sleeve ll. The assembly [8 comprises a portion 20 integral with the piston 8, a portion l9 secured thereto and a cuff 2i lying within the assembly [8 and formed with a flange 22 to be received between the parts l9 and 20 so that cuff 2| moves with piston 8. The free end of the part l9 has an internal diameter greater than the external diameter of the sleeve I? so that there is an annular space 29 between them. The end face 23 of the part i9 is adapted to engage the flight-safety stop for a purpose which will later be described, and similarly the end face 24 of the and 2| is adapted to engage the fine pitch stop.

Lying within the sleeve ll are two sets of axially-extending, resilient fingers 25, 26 which are circumferentially spaced around the sleeve Ii (see Figure 2). Each finger 25 is integrally formed with a projection 21 and each finger 26 is integrally formed with a projection 28. Both sets of projections extend radially outwardly beyond the sleeve H to lie in the path of travel of the flange assembly IS. The projections 27 are so arranged in relation to the annular space 29 that they pass freely into said space-whereas the projections 28 (since they lie radially outwardly beyond the projections 2?) are arranged to engage the end face 23. As is evident from Figure 3 the projections 27 will engage the end face 24 of the cuff 2| although, as later described, this occurs only after the projections 23 have been displayed relatively to the end face 23 to pass into space 29. The projections 23 constitute the first or fiigbht-safety stop referred to above and the projections 27 constitute said second or fine-pitch stop.

The ends of the spring fingers 25 and 26 which carry their projections tend to collapse radially inwardly and are normally supported so that both lie in the path of travel of flange I8 by a common piston member (the stop piston) generally indicated at 3B. The stop piston 39 has a cylindrical surface 3| which is engaged by the inner faces of the projections 2'! and 28- it will be noted that the projections 21 are extended at 32. With the stop piston Si; in the position shown in Figure 4 the projections 27, 28 are held in the path of travel of the flange assembly i8 and it Will be appreciated that if the stop piston 3 is axially displaced to a sufficient extent the fingers 25 and 26 withdraw the projections 2? and 28 out of the path of travel of flange assembl 18.

The extensions 32 of the projections 2? ensure that the surface 3! holds fingers 25 out for a greater axial travel of stop piston than fingers 25, Accordingly, when the piston 3i? is first displaced to the right (from the position shown in Figure 4 to that shown in Figure 3) the surface 3! first disengages the projections 28 and thereafter with further displacement of the piston 36, it will disengage the projections 21.

The piston 36 is urged by a spring 33 to a position in which it holds the projections 21 and 28 in the path of travel of the piston flange assembly l8.

Pressure fluid from the pipe II i delivered to a cavity as and passes therefrom through one or more holes 35 into the cylinder iii to act on the piston 8 and urge it towards the left as seen in Figure 3. A manual control regulates the de- 4 livery of pressure fluid from a source of supply 46 along duct 36 and into space 3! to act on the piston member 30 and urge it towards the right against spring 33.

The spring 33 extends between the piston member 30 and a ring 38 which carries the fingers 26. The ring 38 co-operates with projections 39 each of which is formed at one end of a resilient finger 66. The fingers iii are carried by a ring dl. The projections 39 lie in the path of travel of a sleeve 42 which is movable with the piston member 3!). The projections 39 are urged radially outwardly by the resilience of fingers 43, and are normally prevented from doing so by the ring 38. However, if the latter is displaced to disengage the projections 39 the latter move clear of the sleeve 42. As shown in Figure 4 the sleeve 62 is capable of moving to the right by the amount a: and this distance is so selected that prior to the sleeve d2 engaging the projections 39 the surface 3i will disengage the projections 28 the projections 27 remaining supported by the surface 8!. The projections 39 constitute the restraint means referred to above.

The piston member 38 is also urged to a position in which the surface 3| sup-ports projections 27 and 25 by a spring 43 extending between the piston member EQ and a stationary part 44 of the hub assembly.

With the arrangement described, when hydraulic fluid under pressure is delivered to the chamber 3 it passes into the cylinder iii and acts on the piston 8 whereby the latter i urged towards the left to move the blades in the finepitch direction and such movement is permitted until the end face 2-3 engages the projections 28 whereupon piston 8 is prevented from further travel in this direction. The projections 28 constitute the flight-safety stop. When pressure fluid is delivered through passage 35 into chamber 37 (at the discretion of the operator) it acts on the piston member 39 to move it axially against springs 33 and 43 so that surface 3! disengages the projections 23 whereby the resilient fingers 26 collapse radially inwardly and carry the projections 28 out of the path of travel of the end face 23. Consequently the piston 8 is freed for further movement towards the left to carry the blades within the first extended range. The piston 38, it pressure oil supplying means .48 and the control 45 in combination with the resilient fingers 25 constitute the release means for displacing the flight-safety stop as just described. The movement of the piston member 3E3 towards the right thereby disengaging the surface 3! from the projections 28 has brought the sleeve 32 against restraint means comprising the projections 39 so that the piston member 39 is prevented from further movement. Consequently the surface 3| remains in contact with the projections 27 to hold them in a position to engage the end face 2 and limit the extended travel of the piston 8 to the left. These conditions prevail until the end face 24 is brought against the projections 27 and, by the deliberate action of the operator, hydraulic fluid is delivered from chamber St to the cylinder it so that pressure within the cylinder is built up. The build up in pressure acting on the piston 8 is applied as an axial thrust to the end face 2 2 and so to the projections 21. When this axial face attains a value sufficient to overcome spring 33 the fingers 25 are moved, with piston 8, towards the left whereby the ring 38 is carried clear of the projections 39 and fingers 40 spring outwardly (as shown in Figure 3) to carry the projections 39 out of the path of travel of the sleeve 42. The piston member 39 is then free to move further to the right and this occurs when pressure fiuid is delivered through passage 36 to chamber 31. With such further movement of the piston member 39, the surface 3| is carried clear of the projections 2'! so that the resilient fingers are enabled to collapse radially inwardly whereby the projection 2'! disengage the end face 24. The flange assembly 88 is thus freed and the piston 8 is enabled to travel towards the left beyond the fine-pitch stop into the second extended range.

When the blades are returned, firstly, from the second pitch range into the first pitch range and, secondly into the normal pitch range the flange assembly It passes readily over the projections 27 and 28. This movement is preceded by release of pressure in the chamber 31 whereby piston member 39 is returned by springs 33, 43 to its normal position and the projections 21 and 28 are returned to lie in the path of travel or" the flange assembly 18, the fingers being pushed radially outwardly by piston 39 which, as shown in Figure 4, is formed with inclined surfaces up which the finger may readily ride to be pushed outwardly. Movement of the piston 8 into the normal pitch range enables the fingers 25 and ring 38 to be returned to spring 33 to a position in which the ring 38 engages projections 39 and returns them into the path of travel of the sleeve 42. The projections 21 and 29 are thus automatically returned to their operative positions when the blades are returned to their normal pitch range.

I claim:

1. In a variable-pitch propeller having a hub, a hydraulic cylinder and piston means within said hub, said hub being adapted to receive propeller blades the pitch of which may be varied and connecting means between said piston means and said propeller blades to adjust said blades within a range of normal operation, within a first range extending beyond said normal range and within a second range extending beyond the first extended range, a first stop means within said hub positioned to be engaged by the piston means to prevent movement of the blades beyond the normal pitch range, a second stop means within said hub operatively associated with said piston means after said piston means has passed said first stop to prevent its travel beyond said first extended range, stop displacing means operatively associated with said first and second stop means for displacing said stops in succession, restraint means within said hub operatively associated with said stop displacing means for normally preventing said stop displacing means from acting to displace said second stop means, and restraint by-pass means positioned within said hub and operatively associated with said piston means and second stop means whereby upon engagement of said second stop means by said piston means the said restraint means is rendered inoperative,

2. A variable-pitch propeller as claimed in claim 1 wherein the first and second stops comprise projections movable into and out of the path of travel of said piston means and wherein the means for displacing said stop projections comprises resilient fingers upon which are carried said projections and which urge them into and out of the path of said piston means and being common to both said first and second stops, the member holding said projections against displacement by their fingers, said member being movable relatively to said projections to release them, the said first stop projection being released upon completion of the first part of its movement and the said second stop projection on completion of the second part of its movement.

3. A variable-pitch propeller as claimed in claim 2 in which said holding member is a stop piston within said hub and positioned to move axially of said hub, the said stop piston being spring urged to hold said stop projections in the path of travel of said piston means.

4. A variable-pitch propeller as claimed in claim 3 in which said stop piston is operated hydraulically to release said stop projections independently of the operation of said hydraulic cylinder and piston means.

5. A variable-pitch propeller as claimed in claim 4 wherein said stop piston is normally prevented from performing the second part of its movement by said restraining means which comprises one or more projections in the path of said stop piston, each projection being carried by a restraint finger which urges the projection out of the path of said stop piston and being held against such displacement by said restraint by-pass means.

6. A variable-pitch propeller as claimed in claim 5 in which said restraint by-pass means comprises a movable ring member positioned to engage a plurality of stop piston projections, said member carrying the resilient fingers comprising said second stop.

7. A variable-pitch propeller as claimed in claim 6 wherein spring means urges said ring member to engage said stop piston projections.

8. A variable-pitch propeller as claimed in claim '7 wherein said spring means comprises a compression spring held between said stop piston and said ring member.

9. A variable-pitch propeller as claimed in claim 8 in which said ring member is moved to disengage said stop piston projections by said piston element upon the hydraulic pressure in said hydraulic cylinder and piston means exceeding a preselected Value.

10. A variable-pitch propeller as claimed in claim 9 wherein said first stop projection is engageable by an end face of a cylindrical flange assembly of said piston means, said projection on displacement being accommodated within the flange assembly in which is also accommodated said second stop projection and which is formed with an internal stepped end face to engage the second stop projection.

SIDNEY PHILIP BASEVI.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,433,990 Hardy Jan. 6, 1948 2,477,868 Forman Aug. 2, 1949 2,542,463 Beard Feb. 20, 1951 FOREIGN PATENTS Number Country Date v 590,913 Great Britain July 31, 1947 

